JP2018120651A - Spark plug - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a spark plug which enables the suppression of the interface peeling of a buffer layer and a discharge layer.SOLUTION: A spark plug comprises: a first electrode including a chip arranged by bonding a discharge layer including Pt as a primary component and a buffer layer including Pt as a primary component to each other, and an electrode base material made of an alloy including Ni as a primary component, or Ni; and a second electrode opposed to the first electrode through a spark gap. The buffer layer is composed of an alloy including Ni as a second component and having a thickness of 0.05 mm or more, and welded to the electrode base material. The discharge layer is composed of an alloy including Rh as a second component. As to the organization of the discharge layer and buffer layer of the chip after welding to the electrode base material, the discharge layer and the buffer layer are different from each other in average crystal grain diameter.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a spark plug, and more particularly to a spark plug in which a chip mainly composed of Pt is provided on an electrode.

  In order to improve the spark wear resistance of the electrode, a spark plug is known in which a first electrode in which a chip mainly composed of Pt is bonded to an electrode base material and a second electrode are opposed to each other. Patent Document 1 discloses a technique using a chip in which a discharge layer made of a Pt—Ir alloy is bonded to a relaxation layer made of a Pt—Ni alloy in order to alleviate thermal stress caused by the thermal expansion difference between the chip and the electrode base material. It is disclosed.

JP-A-6-60959

  However, in the conventional technique described above, there is a problem of interfacial delamination between the electrode base material and the relaxation layer and interfacial delamination between the relaxation layer and the discharge layer due to thermal stress due to thermal shock or the like.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a spark plug capable of suppressing interfacial peeling between a relaxation layer and a discharge layer.

  In order to achieve this object, in the spark plug of the present invention, the first electrode has a tip in which a discharge layer mainly composed of Pt and a relaxation layer mainly composed of Pt, and an alloy mainly composed of Ni or Ni. An electrode base material. The second electrode and the first electrode face each other through the spark gap. The relaxation layer is made of an alloy containing Ni as a second component and having a thickness of 0.05 mm or more, and is welded to the electrode base material. The discharge layer is made of an alloy containing Rh as the second component. In the structure of the discharge layer and the relaxation layer of the chip after being welded to the electrode base material, the average crystal grain size of the discharge layer and the average crystal grain size of the relaxation layer are different from each other.

  According to the spark plug of claim 1, since the relaxation layer mainly composed of Pt is made of an alloy containing Ni as a second component and having a thickness of 0.05 mm or more, it is made of an alloy mainly containing Ni or Ni. The thermal stress caused by the thermal expansion difference between the electrode base material and the discharge layer made of an alloy containing Pt as a main component and Rh as the second component is relaxed.

  Further, the structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material is different from each other in the average crystal grain size of the discharge layer and the average crystal grain size of the relaxation layer. The thermal stress can be relieved by causing cracks at the grain boundaries. As a result, there is an effect that the interface peeling between the electrode base material and the relaxing layer and the interface peeling between the relaxing layer and the discharge layer can be suppressed.

  According to the spark plug according to claim 2, in the structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material, the average crystal grain size of the discharge layer is larger than the average crystal grain size of the relaxation layer. Therefore, the thermal stress can be relaxed by causing cracks in the crystal grain boundaries of the discharge layer due to the thermal stress. Therefore, in addition to the effect of the first aspect, there is an effect that the interfacial peeling can be further suppressed.

  According to the spark plug of claim 3, the value obtained by dividing the thickness of the discharge layer after the tip is welded to the electrode base material by the thickness of the relaxation layer after the tip is welded to the electrode base material is Less than 3. As a result, in addition to the effect of the second aspect, the discharge layer can be easily deformed by the thermal stress, and the relaxation effect of the thermal stress can be ensured.

  According to the spark plug of claim 4, in the structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material, the average crystal grain size of the discharge layer is smaller than the average crystal grain size of the relaxation layer. Therefore, it is possible to easily cause cracks in the crystal grain boundaries of the relaxation layer due to thermal stress. As a result, in addition to the effect of the first aspect, there is an effect that the thermal stress is relaxed by the crack of the grain boundary of the relaxation layer, and the interface peeling can be suppressed.

  According to the spark plug of claim 5, since the relaxation layer contains more than 3% by mass of Ni, the linear expansion coefficient of the relaxation layer is expressed by the linear expansion coefficient of the discharge layer and the linear expansion coefficient of the electrode base material. It can be close to the middle. As a result, in addition to the effect of the fourth aspect, there is an effect that the interfacial peeling can be further suppressed.

  According to the spark plug of claim 6, the composition of the discharge layer and the relaxation layer is such that the average crystal grain size of the discharge layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ° C. for 33 hours is It is set to be larger than the average crystal grain size of the relaxation layer. Therefore, in addition to the effect of any one of claims 1 to 5, in the environment where the first electrode is heated to about 1000 ° C. in the combustion chamber, it is easy to cause minute cracks at the crystal grain boundaries of the discharge layer. This is effective in reducing thermal stress.

  According to the spark plug of claim 7, the composition of the discharge layer and the relaxation layer is such that the average crystal grain size of the discharge layer in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ° C. for 33 hours, It is set to be smaller than the average crystal grain size of the relaxation layer. Therefore, in addition to the effect of any one of claims 1 to 5, in an environment where the first electrode is heated to about 1000 ° C. in the combustion chamber, it is possible to easily cause cracks in the crystal grain boundaries of the relaxation layer, It has the effect of reducing thermal stress.

  According to the spark plug of the eighth aspect, since the discharge layer contains Pt and Rh in an amount of 85% by mass or more, in addition to the effect of any one of the first to seventh aspects, there is an effect that the spark wear resistance can be improved.

It is a half sectional view of the spark plug in one embodiment of the present invention. It is sectional drawing of a center electrode and a ground electrode.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a side sectional view of a spark plug 10 according to an embodiment of the present invention, and FIG. 2 is a sectional view of a center electrode 13 and a ground electrode 18. 1 and 2, the lower side of the drawing is referred to as the front end side of the spark plug 10, and the upper side of the drawing is referred to as the rear end side of the spark plug 10.

  As shown in FIG. 1, the spark plug 10 includes an insulator 11, a center electrode 13 (second electrode), a metal shell 17, and a ground electrode 18 (first electrode). The insulator 11 is a substantially cylindrical member formed of alumina or the like that is excellent in mechanical properties and insulation at high temperatures. The insulator 11 passes through the shaft hole 12 along the axis O.

  The center electrode 13 is a rod-shaped electrode that is inserted into the shaft hole 12 and held by the insulator 11 along the axis O. The center electrode 13 includes an electrode base material 14 and a chip 15 joined to the tip of the electrode base material 14. The electrode base material 14 is embedded with a core material excellent in thermal conductivity. The electrode base material 14 is made of an alloy mainly composed of Ni or a metal material made of Ni, and the core material is made of copper or an alloy mainly composed of copper. The tip 15 is made of a noble metal such as platinum, iridium, ruthenium, or rhodium that has a higher resistance to spark consumption than the electrode base material 14 or an alloy mainly composed of a noble metal.

  The terminal fitting 16 is a rod-like member to which a high voltage cable (not shown) is connected, and the distal end side is disposed in the insulator 11. The terminal fitting 16 is electrically connected to the center electrode 13 in the shaft hole 12. The metal shell 17 is a substantially cylindrical metal member fixed to a screw hole (not shown) of the internal combustion engine. The metal shell 17 is fixed to the outer periphery of the insulator 11.

  The ground electrode 18 includes an electrode base material 19 joined to the metal shell 17 and a chip 20 joined to the electrode base material 19. The electrode base material 19 is embedded with a core material excellent in thermal conductivity. The electrode base material 19 is made of an alloy mainly composed of Ni or a metal material made of Ni, and the core material is made of copper or an alloy mainly composed of copper. It is naturally possible to omit the core material and form the entire electrode base material 19 with an alloy mainly composed of Ni or a metal material made of Ni. The electrode base material 19 is bent toward the center electrode 13, and the tip 20 faces the center electrode 13 through a spark gap G (see FIG. 2).

  The spark plug 10 is manufactured by the following method, for example. First, the center electrode 13 is inserted into the shaft hole 12 of the insulator 11. The center electrode 13 is disposed such that the tip is exposed to the outside from the shaft hole 12. After the terminal fitting 16 is inserted into the shaft hole 12 and the conduction between the terminal fitting 16 and the center electrode 13 is ensured, the metal shell 17 to which the electrode base material 19 has been joined in advance is assembled to the outer periphery of the insulator 11. After joining the tip 20 to the electrode base material 19, the electrode base material 19 is bent so that the tip 20 faces the center electrode 13 in the direction of the axis O to obtain the spark plug 10.

  As shown in FIG. 2, the chip 20 is a clad material including a relaxation layer 21 and a discharge layer 22 laminated on the relaxation layer 21, and is formed in a disk shape. The discharge layer 22 is metallurgically joined to the relaxation layer 21 by various methods such as a rolling method, an explosion method, a diffusion method, and an explosion rolling method. In the tip 20, the relaxation layer 21 is joined to the electrode base material 19 by resistance welding or the like.

  The discharge layer 22 is an alloy containing Pt as a main component and Rh as a second component. When the discharge layer 22 contains Pt and Rh, it is possible to ensure oxidation resistance and spark consumption resistance. Note that “consisting mainly of Pt” means that the content ratio of Pt with respect to the discharge layer 22 is 50 mass% or more. The discharge layer 22 can contain a third component such as Ni, Cr, Ti, Si, Y, and Sr in addition to Pt and Rh. The discharge layer 22 preferably contains 85% by mass or more of Pt and Rh. This is to improve the spark wear resistance.

  The relaxation layer 21 is an alloy having a thickness of 0.05 mm or more containing Pt as a main component and Ni as a second component. The relaxation layer 21 is interposed between the electrode base material 19 and the discharge layer 22 to relieve thermal stress caused by the thermal expansion difference between the electrode base material 19 and the discharge layer 22. “Mainly containing Pt” means that the content of Pt with respect to the relaxation layer 21 is 50 mass% or more. The relaxing layer 21 preferably contains more than 3% by mass of Ni. This is to ensure a thermal stress relaxation effect by the relaxation layer 21.

  Since the relaxing layer 21 has a thickness of 0.05 mm or more, the weldability between the electrode base material 19 and the relaxing layer 21 can be secured. On the other hand, when the thickness of the relaxation layer 21 is 0.05 mm or more, interface peeling or relaxation between the electrode base material 19 and the relaxation layer 21 due to thermal stress caused by the thermal expansion difference between the electrode base material 19 and the discharge layer 22. Interfacial peeling between the layer 21 and the discharge layer 22 is likely to occur. When the interface peeling occurs, the discharge layer 22 and the chip 20 are lifted, so that the spark gap G is reduced and the ignitability of the spark plug 10 is impaired. Further, when the interfacial peeling progresses and the discharge layer 22 and the chip 20 fall off, the spark gap G increases, and the ignitability of the spark plug 10 is also impaired. Such interfacial debonding may occur due to thermal shock having a maximum temperature of about 600 to 1000 ° C.

  In order to suppress interfacial peeling, the average crystal grain size of the relaxation layer 21 and the discharge layer 22 is controlled. When the crystal grain size is large, the range (length) in which the transition is accumulated increases, and the number of transitions that accumulate is also increased. As a result, stress concentration can easily occur, and cracks can easily occur in the crystal grain boundaries. That is, by making the average crystal grain size of the relaxation layer 21 different from the average crystal grain size of the discharge layer 22, cracks occur in the crystal grain boundaries of the layer having the larger average crystal grain size among the relaxation layer 21 and the discharge layer 22. To relieve thermal stress and suppress interfacial debonding. The crystal grain sizes of the relaxation layer 21 and the discharge layer 22 can be adjusted by controlling the processing conditions and composition of the relaxation layer 21 and the discharge layer 22.

  Since the structure of the relaxation layer 21 made of PtNi alloy or the discharge layer 22 made of PtRh alloy hardly changes at a temperature of about 600 ° C., the structure of the relaxation layer 21 and the discharge layer 22 after being welded to the electrode base material 19 In addition, it has a great influence on the relaxation of thermal stress due to thermal shock with a maximum temperature of about 600 ° C. The structure of the relaxation layer 21 and the discharge layer 22 after being welded to the electrode base material 19 can be controlled by the processing conditions of the relaxation layer 21 and the discharge layer 22.

  On the other hand, when the relaxation layer 21 and the discharge layer 22 are heated to about 1000 ° C., the structure changes with time and the average crystal grain size changes. The structure of the relaxation layer 21 and the discharge layer 22 at this time can be controlled by the composition of the relaxation layer 21 and the discharge layer 22. The structure of the relaxation layer 21 and the discharge layer 22 controlled by the composition of the relaxation layer 21 and the discharge layer 22 has a great influence on the relaxation of thermal stress due to thermal shock having a maximum temperature of about 1000 ° C.

  The average crystal grain size of the relaxation layer 21 and the discharge layer 22 is determined in accordance with Annex C “Evaluation by Cutting Method” of JIS G0551 (2013) created based on ISO643 (2003 edition). The average crystal grain size is an average line segment length per crystal grain of a test line that crosses the inside of a crystal grain appearing on a flat cross section of a test piece polished for microscopic observation. In the present embodiment, one or more straight test lines parallel to the axis O, a straight test line orthogonal to the axis O, and a straight test line intersecting with the axis O at 45 ° are drawn on the cross section including the axis O. The average crystal grain size is obtained. From the average number of captured crystal grains per 1 mm of the test line or the number of average intersections per 1 mm of the test line, the average line segment length per crystal grain of the test line crossing the crystal grain is obtained. The number of captured crystal grains is the number of crystals passed or captured by the test line, and the number of intersections is the number of intersections between the grain boundaries and the test lines.

  In the structure of the discharge layer 22 and the relaxation layer 21 after being welded to the electrode base material 19, if the average crystal grain size of the relaxation layer 21 and the average crystal grain size of the discharge layer 22 are the same, However, there is a problem that the interface peeling between the electrode base material 19 and the relaxing layer 21 and the interface peeling between the relaxing layer 21 and the discharge layer 22 are likely to occur due to thermal shock of about 600 ° C.

  On the other hand, when the average crystal grain size of the discharge layer 22 is larger than the average crystal grain size of the relaxation layer 21 in the structure of the discharge layer 22 and the relaxation layer 21 after being welded to the electrode base material 19, However, the thermal shock of about 600 ° C. can cause cracks in the crystal grain boundaries of the discharge layer 22 to easily deform the discharge layer 22 (chip 20). As a result, thermal stress can be relieved by cracks in the grain boundaries of the discharge layer 22 and deformation of the discharge layer 22 (chip 20), and interface peeling can be suppressed.

  Note that if the crystal grain boundaries of the discharge layer 22 are cracked and the crystal grains fall off, the ignitability of the spark plug 10 may be impaired. However, the deformation of the discharge layer 22 (chip 20) can reduce the degree of cracks at the grain boundaries, so that the cracks at the grain boundaries of the discharge layer 22 do not adversely affect the ignitability of the spark plug 10. it can.

  Further, in the structure of the discharge layer 22 and the relaxation layer 21 after being welded to the electrode base material 19, if the average crystal grain size of the discharge layer 22 is smaller than the average crystal grain size of the relaxation layer 21, the maximum temperature reached 600. Cracks can be generated at the crystal grain boundaries of the relaxation layer 21 by a thermal shock of about ° C. As a result, the thermal stress can be relaxed by the cracks in the crystal grain boundaries of the relaxation layer 21, and the interface peeling can be suppressed. Since relaxation layer 21 is not a part responsible for performance such as electric discharge, even if cracks occur in the crystal grain boundaries of relaxation layer 21, the ignitability of spark plug 10 can be prevented from being adversely affected.

  Further, in the structure of the discharge layer 22 and the relaxation layer 21 after the chip 20 is heated at 1200 ° C. for 33 hours, the average crystal grain size of the discharge layer 22 is that of the relaxation layer 21. If it is set to be larger than the average crystal grain size, it is possible to easily cause cracks in the crystal grain boundaries of the discharge layer 22 due to thermal shock with a maximum temperature of about 1000 ° C. As a result, thermal stress can be relaxed and interface peeling can be suppressed.

  Further, in the structure of the discharge layer 22 and the relaxation layer 21 after the chip 20 is heated at 1200 ° C. for 33 hours, the average crystal grain size of the discharge layer 22 is that of the relaxation layer 21. When set so as to be smaller than the average crystal grain size, it is possible to easily cause cracks at the crystal grain boundaries of the relaxing layer 21 by thermal shock with a maximum temperature of about 1000 ° C. As a result, thermal stress can be relaxed and interface peeling can be suppressed.

  The thicknesses of the discharge layer 22 and the relaxation layer 21 are the thicknesses of the discharge layer 22 after the tip 20 is welded to the electrode base material 19 and the relaxation layers after the tip 20 is welded to the electrode base material 19. The value divided by the thickness of 21 is preferably less than 3. This is because by making the thickness of the discharge layer 22 less than 3 with respect to the thickness of the relaxation layer 21, the discharge layer 22 can be easily deformed by thermal stress, and the thermal stress relaxation effect is ensured. The thicknesses of the discharge layer 22 and the relaxation layer 21 are the thicknesses of the center of the discharge layer 22 and the relaxation layer 21 in the cross section including the axis O.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

<Create sample>
The tester produced various chips 20 having different shapes, compositions of the discharge layer 22 and the relaxation layer 21, average crystal grain size and thickness by solid phase diffusion bonding of the discharge layer 22 and the relaxation layer 21. The discharge layer 22 was joined to the electrode base material 19 made of NFC600 by resistance welding, and samples of the spark plug 10 in which various tips 20 were provided on the ground electrode 18 were prepared. The created samples are listed in Table 1. Since a plurality of evaluations were performed for each sample, a plurality of each sample was prepared.

なお、サンプル１〜５６は、クラッド材料で放電層２２及び緩和層２１が作られたチップ２０が接地電極１８に設けられている。サンプル５７〜６２は、放電層２２と緩和層２１とに分かれていないチップが接地電極１８に設けられている。表１におけるチップの「放電層」「緩和層」の欄の数値は元素の質量％を示している。

In samples 1 to 56, the chip 20 in which the discharge layer 22 and the relaxation layer 21 are made of a clad material is provided on the ground electrode 18. In Samples 57 to 62, a chip that is not divided into the discharge layer 22 and the relaxation layer 21 is provided on the ground electrode 18. The numerical values in the “discharge layer” and “relaxation layer” columns of the chip in Table 1 indicate the mass% of the element.

  The tester has two types of tests for evaluating the spark wear resistance (Test 1 and Test 2), and two types of repeated cooling tests (cooling test 1 and test 2) in which the ground electrode 18 is heated by a burner and allowed to cool. A cold test 2) was performed on each sample separately.

  In addition to these tests, the tester embeds the chip 20 before the test after being welded to the electrode base material 19 in the resin, polishes it, and appears on a cross section including the axis O by microscopic observation. The average line segment length (average crystal grain size) per crystal grain of a test line (one or more straight lines each parallel to, perpendicular to, and 45 ° to the axis O) crossing the crystal grain was determined. Values obtained by dividing the average crystal grain size of the discharge layer 22 by the average crystal grain size of the relaxation layer 21 are shown in the columns “Crystal grain size” and “Previous” in Table 1. At the same time, a value obtained by dividing the thickness of the discharge layer 22 appearing on the cross section including the axis O by the thickness of the relaxation layer 21 was obtained. The value is shown in the column of “Thickness” in Table 1.

  Separately, the tester cut the electrode base material 19 before the test, to which the tip 20 was welded. The cut electrode base material 19 and the chip 20 are heated at 1200 ° C. for 33 hours, and then the electrode base material 19 and the chip 20 embedded in the resin are polished, and the inside of the crystal grains appearing on the cross section including the axis O The average line segment length (average crystal grain size) per crystal grain of the test line across (one or more straight lines each parallel to, perpendicular to, and 45 ° with respect to the axis O) was determined. Values obtained by dividing the average crystal grain size of the discharge layer 22 by the average crystal grain size of the relaxation layer 21 are shown in the “crystal grain size” and “after” columns of Table 1.

<Spark Resistance Consumption Test 1 Test Method and Evaluation Method>
The tester attached each sample of the spark plug 10 to a 4-cylinder direct injection engine with a displacement of 2.0 liters equipped with an exhaust turbine supercharger and operated the engine. The spark gap (interval between the discharge layer 22 and the center electrode 13) of each sample was 0.75 mm. The engine operating conditions were a rotational speed of 4000 rpm, an air fuel ratio of 12.0, a load of 190 kPa as a mean effective effective pressure (NMEP), and an engine operating time of 200 hours.

  The tester measured the spark gap of each sample after the test with a pin gauge, and obtained the increase amount (consumption amount) of the spark gap by the test. The evaluation was “A” when the increase amount was less than 0.15 mm, “B” when the increase amount was 0.15 mm or more and less than 0.20 mm, and “C” when the increase amount was 0.20 mm or more.

<Spark Resistance Consumption Test 2 Test Method and Evaluation Method>
An engine equipped with each sample of the spark plug 10 was operated in the same manner as in Test 1 except that the spark gap of each sample was 1.05 mm.

  The tester measured the spark gap of each sample after the test with a pin gauge, and obtained the increase amount (consumption amount) of the spark gap by the test. Evaluation is “S” when the increase is less than 0.15 mm, “A” when the increase is from 0.15 mm to less than 0.20 mm, “B” when the increase is from 0.20 mm to less than 0.30 mm, and the increase is “C” was set for 0.30 mm or more.

<Test method of the thermal test 1>
The tester, after heating with a burner for 2 minutes so that the temperature of the tip of the electrode base material 19 (the part farthest from the metal shell 17) is 600 ° C., let it cool for 1 minute as one cycle, 1000 cycles were applied to the electrode matrix 19.

<Test method of the thermal test 2>
The tester added 1000 cycles to the electrode base material 19 by heating the tip of the electrode base material 19 with a burner for 2 minutes so that the temperature was 1000 ° C., and letting it cool for 1 minute as one cycle. .

<Evaluation method of interface peeling>
The tester embedded the ground electrode 18 after the test in a resin and polished it to expose the cross section including the center of the chip 20. By microscopic observation, the length of the tip 20 (a dimension along the interface between the tip 20 and the electrode base material 19) is A, and the portion where the interface layer is not peeled and the relaxing layer 21 and the electrode base material 19 are joined Where a is the length of the part where the interface peeling does not occur and the length of the portion where the discharge layer 22 and the relaxation layer 21 are joined is b, and the ratio of the interface peeling, that is, X = (A−a) / A ( %), Y = (A−b) / A (%). Evaluation is such that the larger value of X and Y is less than 10% is “S”, 10% to less than 40% is “A”, 40% to less than 50% is “B”, and 50% or more is “C”. did.

<Evaluation method of intergranular cracking>
The tester evaluated each of the discharge layer 22 and the relaxation layer 21 in the cross-section (the cross-section including the center of the chip 20 exposed by embedding the ground electrode 18 after the test in resin and polishing) in the cross-section evaluated for the above-described interface peeling. The ratio (%) of the area of the part missing due to the grain boundary cracking with respect to the cross-sectional area was determined. The evaluation was “A” for less than 1%, “B” for 1% or more and less than 10%, and “C” for 10% or more.

<Method for evaluating deformation>
The deformation of the chip 20 is obtained by subtracting the protrusion amount of the tip 20 from the electrode base material 19 measured with the micrometer before the cooling test from the protrusion amount of the tip 20 from the electrode base material 19 measured with the micrometer after the cooling test. Amount (μm).

<Method of comprehensive evaluation>
For each evaluation, 3 points were assigned to “S”, 2 points were given to “A”, 1 point was given to “B”, and 0 points were given to C. Each evaluation was digitized to calculate a total score. In the comprehensive evaluation, the total score was “S” for 18 points or more, “A” for 15 to 17 points, “B” for 11 to 14 points, and “C” for 0 to 10 points. However, when at least one “C” is present in each evaluation, the overall evaluation is “C” regardless of the total score.

<Result>
As shown in the “chip” and “composition” columns of Table 1, Samples 1 to 52 were samples in which the discharge layer was made of a PtRh alloy and the relaxation layer was made of a PtNi alloy. In Samples 53 and 54, the relaxation layer was made of a PtNi alloy, but the discharge layer was made of a metal other than the PtRh alloy. In Samples 55 and 56, the discharge layer was made of a PtRh alloy, but the relaxation layer was made of a metal other than the PtNi alloy. Samples 57 to 62 were samples using chips that were not clad materials.

  In the evaluation of interfacial debonding in the thermal test 1, the samples 53 to 56, 57, 59, 60, and 62 were evaluated as C, whereas the samples 1 to 14, 17 to 52, 58, and 61 were evaluated as S to B. Among these samples 1 to 14, 17 to 52, 58 and 61, the samples 1 to 14 and 17 to 52 other than the samples 58 and 61 were evaluated as A or B in the spark wear resistance test 1.

  Among the samples 1 to 52, as shown in the columns of “Crystal grain size” and “Previous” in Table 1, samples 15 and 16 are the average crystal grain size of the discharge layer 22 after being welded to the electrode base material 19. The average crystal grain size of the relaxation layer 21 was the same. Samples 1 to 14 and 17 to 52 were samples in which the average crystal grain size of the discharge layer 22 after being welded to the electrode base material 19 and the average crystal grain size of the relaxation layer 21 were different. In samples 1 to 14 and 17 to 52, in which the discharge layer is made of a PtRh alloy and the relaxation layer is made of a PtNi alloy, the average crystal grain size and relaxation of the discharge layer 22 after being welded to the electrode base material 19 It was confirmed that interfacial delamination can be suppressed in the thermal test 1 where the maximum temperature reached 600 ° C. by making the average crystal grain size of the layer 21 different from each other.

  Among samples 1 to 14 and 17 to 52, samples 1 to 14 are samples in which the average crystal grain size of the discharge layer 22 after being welded to the electrode base material 19 is smaller than the average crystal grain size of the relaxation layer 21. It was. Samples 17 to 52 were samples in which the average crystal grain size of the discharge layer 22 after being welded to the electrode base material 19 was larger than the average crystal grain size of the relaxing layer 21. In samples 1 to 14, it was found in the thermal test 1 that the area of grain boundary cracks in the relaxation layer 21 was larger than the area of grain boundary cracks in the discharge layer 22. On the other hand, samples 17 to 52 were found to have a grain boundary crack area of the discharge layer 22 larger than that of the relaxation layer 21 in the cooling test 1.

  From these results, it can be said that the interfacial delamination can be suppressed by relaxing the thermal stress generated by the thermal shock of the cold test 1 due to the intergranular cracking generated in the layer having the large average crystal grain size among the discharge layer 22 and the relaxation layer 21 Inferred.

  In the evaluation of interfacial delamination in the thermal test 1, when samples 8, 9, 17 to 20, 34, and 35 are compared, samples 17 to 20, 34, and 35 in which the Ni content of the relaxation layer 21 is 3% by mass or less are evaluated. Was B. However, the samples 8 and 9 in which the relaxation layer 21 contains more than 3 mass% (5 mass%) of Ni were evaluated as S. From this result, in the relaxation layer 21 containing more than 3% by mass of Ni, the linear expansion coefficient of the relaxation layer 21 approached the middle between the linear expansion coefficient of the discharge layer 22 and the linear expansion coefficient of the electrode base material 19. Thus, it is presumed that interfacial delamination could be suppressed.

  In the evaluation of the interfacial delamination in the thermal test 1, when comparing the samples 31 to 33, the value obtained by dividing the thickness of the discharge layer 22 after being welded to the electrode base material 19 by the thickness of the relaxation layer 21 is 3 or more. 32 and 33 were evaluated as B. However, the samples 29 to 31 in which the value obtained by dividing the thickness of the discharge layer 22 by the thickness of the relaxation layer 21 was less than 3 were evaluated as S. From this result, it is surmised that by reducing the thickness of the discharge layer 22, the discharge layer 22 can be easily deformed by thermal stress, and the effect of mitigating thermal stress can be improved.

  In addition, in the evaluation of the spark wear resistance test 2, when the samples 6, 7, 13, and 14 were compared, the evaluation of the sample 14 in which the discharge layer 22 contained 80% by mass of Pt and Rh was C. However, samples 6, 7, and 13 in which the discharge layer 22 contained Pt and Rh in an amount of 85% by mass or more were evaluated as A or B. Similarly, when the samples 6, 7, 13, and 14 were compared in the evaluation of the spark wear resistance test 1, the sample 14 in which the discharge layer 22 contained 80% by mass of Pt and Rh was evaluated as B. However, Samples 6, 7, and 13 in which the discharge layer 22 contained Pt and Rh in an amount of 85% by mass or more were evaluated as A. From this result, it was found that the spark wear resistance can be improved when the discharge layer 22 contains Pt and Rh in an amount of 85% by mass or more.

  In the evaluation of interfacial peeling and intergranular cracking in the thermal test 2, samples 8 to 12 and samples 13 and 14 are compared, samples 17 to 24 and samples 25 to 33 are compared, and samples 34 to 36 and samples 37 to 36 are compared. 44. In Samples 8 to 12, 17 to 24, and 34 to 36, the average crystal grain size of the relaxation layer 21 after the electrode base material 19 and the chip 20 were heated at 1200 ° C. for 33 hours is larger than the average crystal grain size of the discharge layer 22. It was a big sample. In Samples 13, 14, 25 to 33, and 37 to 44, the average crystal grain size of the discharge layer 22 after heating the electrode base material 19 and the chip 20 at 1200 ° C. for 33 hours is larger than the average crystal grain size of the relaxation layer 21. It was a big sample.

  As a result of comparison, Samples 8 to 12, 17 to 24, and 34 to 36 have larger portions where the relaxation layer 21 is missing due to grain boundary cracking than Samples 13, 14, 25 to 33, and 37 to 44, respectively. It was confirmed. As in Samples 8-12, 17-24, 34-36, the average crystal grain size of the relaxation layer 21 after heating at 1200 ° C. for 33 hours is larger than the average crystal grain size of the discharge layer 22 It was found that by preparing the compositions of the layer 21 and the discharge layer 22, it is possible to easily cause grain boundary cracking in the relaxation layer 21 in the thermal test 2 where the maximum temperature reached 1000 ° C. As a result, thermal stress can be relieved and interface peeling of the chip 20 can be suppressed.

  In addition, it is confirmed that samples 13, 14, 25 to 33, and 37 to 44 have smaller portions where the relaxation layer 21 is lost due to grain boundary cracking than samples 8 to 12, 17 to 24, and 34 to 36, respectively. It was. As in Samples 13, 14, 25 to 33, and 37 to 44, the average crystal grain size of the discharge layer 22 after heating at 1200 ° C. for 33 hours becomes larger than the average crystal grain size of the relaxation layer 21. By preparing the composition of the layer 21 and the discharge layer 22, it is easy to cause minute grain boundary cracks in the discharge layer 22 while suppressing the grain boundary cracks in the relaxation layer 21 in the thermal test 2 where the maximum temperature reached 1000 ° C. I knew it was possible. As a result, thermal stress can be relieved and interface peeling of the chip 20 can be suppressed.

  When the samples 17 to 24 and 34 to 36 are compared with each other in the deformation amount of the cooling test 2, the samples 23, 24, and 36 in which the discharge layer 22 contains the third component are compared with the other samples 17 to 22, 34, and 35. Thus, it was confirmed that the deformation amount can be reduced.

  In this example, various evaluations were performed on samples 1 to 62 in which the chip 20 having a disk or prism shape was provided on the ground electrode 18. According to Samples 1 to 62, it was confirmed that the evaluation result was not affected at all by the shape of the chip 20.

  The present invention has been described above based on the embodiments. However, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the spirit of the present invention. It can be easily guessed.

  In the above embodiment, the case where the shape of the chip 20 is a disk or a prism has been described. However, the shape is not necessarily limited to this, and other shapes can naturally be adopted. Examples of the shape of the other chip 20 include a truncated cone shape and an elliptical column shape.

  In the above embodiment, the case where the tip 20 is joined to the electrode base material 19 by resistance welding has been described. However, the present invention is not necessarily limited to this, and the tip 20 may be joined to the electrode base material 19 by other means. Of course it is possible. Examples of other means include laser welding.

  In the above embodiment, the case where the chip 20 (relaxation layer 21 and discharge layer 22) is provided on the ground electrode 18 has been described, but the present invention is not necessarily limited thereto. It is naturally possible to join the chip 20 to the electrode base material 14 of the center electrode 13 instead of the chip 15 provided on the center electrode 13. Also in this case, the same effect as that described in the above embodiment can be realized.

  In the above embodiment, the case where the electrode base material 19 joined to the metal shell 17 is bent has been described. However, it is not necessarily limited to this. Naturally, instead of using the bent electrode base material 19, it is possible to use a linear electrode base material. In this case, the front end side of the metal shell 17 is extended in the axis O direction, a linear electrode base material is joined to the metal shell 17, and the electrode base material is opposed to the center electrode 13.

  In the above-described embodiment, the case where the axis O of the center electrode 13 and the chip 20 are aligned and the ground electrode 18 is disposed so that the chip 20 faces the center electrode 13 in the direction of the axis O has been described. However, the present invention is not necessarily limited to this, and the positional relationship between the ground electrode 18 and the center electrode 13 can be set as appropriate. Other positional relationships between the ground electrode 18 and the center electrode 13 include, for example, arranging the ground electrode 18 so that the side surface of the center electrode 13 and the ground electrode 18 face each other.

10 Spark plug 13 Metal shell (second electrode)
18 Ground electrode (first electrode)
19 Electrode Base Material 20 Tip 21 Relaxation Layer 22 Discharge Layer

Claims (8)

A first electrode comprising: a chip in which a discharge layer mainly composed of Pt and a relaxation layer mainly composed of Pt are joined; and an electrode base material made of an alloy mainly composed of Ni or Ni and welded to the relaxation layer. When,
A spark plug comprising a second electrode facing the discharge layer via a spark gap,
The discharge layer is made of an alloy containing Rh as a second component,
The relaxation layer is made of an alloy having a thickness of 0.05 mm or more containing Ni as a second component,
The structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material is characterized in that an average crystal grain size of the discharge layer and an average crystal grain size of the relaxation layer are different from each other. Spark plug.   The structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material is characterized in that the average crystal grain size of the discharge layer is larger than the average crystal grain size of the relaxation layer. The spark plug according to claim 1.   The value obtained by dividing the thickness of the discharge layer after the tip is welded to the electrode base material by the thickness of the relaxation layer after the tip is welded to the electrode base material is less than 3. The spark plug according to claim 2.   The structure of the discharge layer and the relaxation layer after the tip is welded to the electrode base material is characterized in that the average crystal grain size of the discharge layer is smaller than the average crystal grain size of the relaxation layer. The spark plug according to claim 1.   The spark plug according to claim 4, wherein the relaxation layer contains more than 3 mass% of Ni.   The composition of the discharge layer and the relaxation layer is such that, in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ° C. for 33 hours, the average crystal grain size of the discharge layer is that of the relaxation layer. The spark plug according to any one of claims 1 to 5, wherein the spark plug is set to be larger than the average crystal grain size.   The composition of the discharge layer and the relaxation layer is such that, in the structure of the discharge layer and the relaxation layer after the chip is heated at 1200 ° C. for 33 hours, the average crystal grain size of the discharge layer is that of the relaxation layer. The spark plug according to any one of claims 1 to 5, wherein the spark plug is set to be smaller than the average crystal grain size.   The spark plug according to any one of claims 1 to 7, wherein the discharge layer contains 85 mass% or more of Pt and Rh.

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